1. Field of the Invention
The present invention relates to spring assemblies for mattresses, cushions and the like and, more particularly, to new and improved methods and apparatus for forming strings of springs enclosed within pockets having flat overlapping side seams and which do not exhibit the disadvantageous condition encountered in prior art assemblies known as false loft.
2. Description of the Prior Art
Numerous techniques have evolved for constructing mattresses, cushions and the like. One such technique which has gained wide acceptance is known as Marshall construction. In this construction, an innerspring assembly comprises the core of the mattress or cushion and is manufactured from a plurality of springs, each individually encapsulated in a pocket of suitable fabric. The pockets of springs are preferably joined together in a string of predetermined length and are arranged in a closely packed array all with their longitudinal axes parallel one to another and with their ends defining a plane. In mattress construction, this array of pocketed springs is typically covered with a quilted foam and fabric pad thereby providing a sleeping surface.
Strings of pocketed coil springs have been manufactured in different ways. In an early method of manufacture, a suitable fabric was folded in half lengthwise and stitched transversely at regular intervals to define pockets into which springs were inserted. This method has largely been replaced in more recent times by a method which uses heat sensitive fabric and ultrasonic welding techniques instead of stitching. An example of strings of pocketed coil springs manufactured by this latter method is disclosed in U.S. Pat. No. 4,234,983, issued to Stumpf and assigned to the common assignee herein. As disclosed in U.S. Pat. No. 4,234,983, a string of pocketed coils is formed by ultrasonically welding the coils into discrete pockets by first folding a heat sensitive fabric in half lengthwise and applying welds transversely to the longitudinal axis of the fabric. Once the coil springs are inserted into the pockets, the pockets are welded closed along a seam running lengthwise of the coil string adjacent one end of the springs. Apparatus for manufacturing the foregoing strings of coils is disclosed, for example, in U.S. Pat. No. 4,439,977, also issued to Stumpf and assigned to the common assignee herein.
A disadvantage of strings of coil springs of the foregoing construction is that the seam running lengthwise of the coil string creates two flaps of excess fabric material at one end of the pocketed springs. Some excess material is necessary along the seam to provide for proper alignment of the string in manufacture and assure adequate strength of the associated welds. However, when the string of coils is arranged to define an innerspring mattress or cushion core, the excess material projecting outwardly of the springs creates a false firmness which is known in the art as "false loft" beneath the outer surface pad of the mattress or cushion. This false loft condition can cause undesirable and objectionable body depressions to form when a user lays on a mattress or cushion.
Attempts have been made to eliminate false loft by constructing a string of coil springs having a flat overlap side seam instead of a top seam. A machine for constructing such coil strings is disclosed, for example, in U.S. Pat. No. 4,986,518, also issued to Stumpf and assigned to the common assignee herein. However, such a machine has a complicated elevator mechanism for spring insertion which has proven to be unreliable under manufacturing conditions.
Accordingly, it has been found to be desirable to provide mattress or cushion constructions in which the innerspring assembly is enclosed within pockets having flat overlap side seams. In particular, it has been found to be desirable to provide such mattress or cushion constructions which do not exhibit false loft by virtue of excess pocketing material adjacent the ends of the coils. Furthermore, it has been found to be desirable to provide coil string assemblies for innerspring constructions which use less pocketing fabric material than has been required in previously known constructions.
Still further, it has been found to be desirable to provide apparatus for constructing pocketed coil strings which are housed within pockets having flat overlap side seams. Such apparatus has been found to be effective, efficient and reliable in use and is structured to be readily retrofitted with existing prior art equipment at an economical cost.